Process for producing water soluble polyamide resins

ABSTRACT

This invention relates to an improved process for producing water soluble polyamide resins at a given reaction location by providing a substantially anhydrous solvent, an aromatic tetracarboxylic dianhydride which is added in excess of its solubility rate within the organic solvent and immediately following is added a quantity of aromatic diamine to produce a polyamide acid precursor which has a greater solubility rate within the organic solvent than the dianhydride; an irreversible formation of aromatic anhydride precipitate is thereby prevented. After formation of the polyamide precursor acid, the precursor is then treated with additional aromatic diamine to form a polymer of controlled imidization, molecular weight and molecular weight distribution. The reaction mass is continuously monitored for viscosity and temperature, and the viscosity of the reaction mass approaches the order of 1,000,000 centipoises. The polymer may thereafter be treated with ammonium hydroxide and other material to render the product water soluble and therefore storable and more advantageous to use all in situ.

i United States Patent Peterson et al.

( 1 June 24, 1975 PROCESS FOR PRODUCING WATER SOLUBLE POLYAMIDE RESINS [75] Inventors: Marvin A. Peterson; Adrian J.

Good; Thaddeus P. Kurek, all of Fort Wayne, Ind.

[731 Assignees: Valspar Inc., Minneapolis, Minn;

General Electric Company, Ft. Wayne, Ind.

[22] Filed: June 4, 1973 {21] Appl. No.: 366,649

I Related U.S. Application Data [63] Continuation of Ser. No. 122,050, March 8, 1971,

abandoned.

[52] U.S. Cl. 260/47 CP; 2601292 N; 260/30.2; 260/30.6 R; 260/30.8 R; 2601308 DS; 260/37.6 N; 260/65; 260/78 TF [51] Int. Cl. C08] 20/32 [58] Field of Search 260/47 CP, 65, 78 TF [56] References Cited UNITED STATES PATENTS 3,505,295 4/1970 Grunsteidl et al. 260/77.5 3,511,807 5/1970 Lovejoy 260/47 3,549,601 12/1970 Fowell 260/78 3,575,891 4/1971 Blane et al 260/25 Primary ExaminerLester L. Lee

[ 5 7 ABSTRACT This invention relates to an improved process for producing water soluble polyamide resins at a given reaction location by providing a substantially anhydrous solvent, an aromatic tetracarboxylic dianhydride which is added in excess of its solubility rate within the organic solvent and immediately following is added a quantity of aromatic diamine to produce a polyamide acid precursor which has a greater solubility rate within the organic solvent than the dianhydride; an irreversible formation of aromatic anhydride precipitate is thereby prevented. After formation of the polyamide precursor acid, the precursor is then treated with additional aromatic diamine to form a polymer of controlled imidization, molecular weight and molecular weight distribution. The reaction mass is continuously monitored for viscosity and temperature, and the viscosity of the reaction mass approaches the order of 1,000,000 centipoises. The polymer may thereafter be treated with ammonium hydroxide and other material to render the product water soluble and therefore storable and more advantageous to use all in situ.

1] Claims, 4 Drawing Figures nU CO PATENTEDJUN 24 I975 SHEET WATER OUT \IISCOMETEQ WATER 1N FIG.

PROCESS FOR PRODUCING WATER SOLUBLE POLYAMIDE RESINS RELATED APPLICATION This application is a continuation-in-whole of US. application Ser. No. [22,050, filed Mar. 8, 1971 and now abandoned entitled PROCESS FOR PRODUC- ING WATER SOLUBLE POLYAMIDE RESINS" invented by Marvin A. Peterson, Adrian J. Good and Thaddeus P. Kurek and assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION In several previously filed co-pending applications, there are disclosed improved interrelated methods for making aromatic polyamic acid materials by synthesizing the polymer from precursor prepolymeric units which in turn are more easily formulated to provide a given molecular structure and composition. This is the teaching of application Ser. No. 822,899, filed May 8, 1969, entitled IMPROVED PROCESS FOR PRO- DUCING WIRE COATING FROM PREPOLYMERIC MATERIALS" and invented by Marvin A. Peterson.

For a teaching relating to control of polymer viscosity, and solution of this type polymer, reference may be made to application Ser. No. 803,037, filed Feb. 27, I969, "IMPROVED PROCESS FOR PRODUCING COATING MATERIALS" and invented by Marvin A. Peterson, which teaches the combination of dianhydride and aromatic diamine which are reacted together within an organic solvent and stabilized by the addition ofa volatile nitrogen containing base, such as ammonia or organic amine with the prepolymer partially imidized before full polymerization to control the viscosity of the solution. In co-pending application Ser. No. 822,899, the reactants are in the form of aromatic dianhydride (X) and aromatic diamine (Y) and are reacted together in anhydrous N-methyl pyrrolidone (NMP) first in the molar ratio of 2/1 to form precursors (XXX) or (YXY), the precursors being then zipped up by adding either (Y) to the (XYX) solution or (X) to the (YXY) solution. A further refinement upon the synthesis technique shown in Ser. No. 822,899 is that indicated in a still further copending application Ser. No. 823,]08, filed May 8, 1969, titled "IMPROVED PRO- CESS FOR PRODUCING POLYAMIDE COATING MATERIALS" now US. Pat. No. 3,663,510 issued May I6, 1972. In Ser. No. 823,108 the precursor material, which is first formulated in the molar ratio of 2/] parts of reactants is zipped up with a slight molar ratio excess of one or the other of the reactants and the resulting product is then back-titrated, approaching a 1/1 molar ratio of reactants. Any preselected desirable molecular weight rangecan be obtained by the back addition of either dianhydride to amine terminated prepolyimide polymer or by the back addition of aromatic diamine to dianhydride terminated prepolyimide polymer. The resulting product can be then endcapped in the manner illustrated in copending application Ser. No. 851,835, filed Aug. 21, 1969, now US. Pat. No. 3,652,500 issued Mar. 28, 1972 titled IMPROVED PROCESS FOR PRODUCING POLYAMIDE COAT- ING MATERIALS BY ENDCAPPING" and invented by Marvin A. Peterson.

When adapting the foregoing teachings to large scale manufacture, we have found it advisable to carry out the reactions within a jacketed vessel which serves as the reaction site for both the precursor formation and the finished polymer. In order to accomplish this, the reaction vessel is unique both in construction and function. For example, because the system is sensitive to the presence of water, the reaction may be carried out under a protective atmosphere and the reaction mass must be temperature and viscosity controlled to be effective in producing the desired product. Also, the preliminary treatment of the reactants and their combination, order and rate of addition are all found to be critical factors which are correlated in the present invention to produce a finished polyamide acid of proven purity and consistency, and which can be manufactured in large quantities.

The finished product has a narrow and consistent range of molecular weight, viscosity and the process is subject to operator control within close limits. One of the difficulties in the manufacture of polyamide acids is how to achieve the necessary temperature control because if reaction temperature is not controlled (and these are all primarily exothermic reactions), imidization will occur to an untoward extent. Also if the reactants are not handled properly and in the manner taught by this invention, such products will precipitate before the chain of reaction is completed and the intermediate products proved difficult to dissolve in solvent, and may have to be discarded. These are the principal difficulties which have proved to be substantial and of long standing in the art; i.e., how to make in a continuous or semi-continuous manner on a large scale, a pollyamide acid which is temperature sensitive, and which must be controlled in viscosity, molecular weight and range of molecular weight. Moreover, it is essential that the process by employed with a view to economy, particularly with a view of conserving expensive solvents which are preferred in the manufacture of polyamide acids.

It has been found that the answer lies in the previously little understood and unexpected factor of: the order of introducing the reactants, the relative proportion of the reactants, the employment of a substantial range of viscosity of reactants, and the strict exclusion of water, both from the reactants and the reaction mass during the operation until a critical period of production. Moreover, it has been discovered that the reaction mass must be carefully and continuously monitored according to temperature and viscosity, and that if the temperature and viscosity are closely correlated with the addition of the reactants, it is possible to produce a finished product of consistency and highly controlled range of molecular weight, degree of imidization, range of viscosity, and it is possible to avoid the loss of reaction batches from time to time which inevitably occurs when the viscosity becomes excessive and the heats of reaction are not carefully controlled.

The present invention proposes a way of overcoming the foregoing described deficiency, and of setting into practice the teachings of the cited pending patent applications in a feasible large manufacturing scale.

OBJECTS OF THE INVENTION The principal object of the present invention is to provide a large scale manufacturing process for producing polyamide acids in uniform quality and molecular weight.

A further object of the present invention is to provide a process which produces polyamide acids on a large scale, and does so by continuously controlling both the temperature and viscosity of material and a novel agitating system, one portion of which is adapted for agitating the reaction mass when it is highly viscous and another agitating means when the reaction mass is less viscous.

A still further object of the present invention is to control the reactants and reaction mass so as to carefully exclude water and the effect of water so that the finished polyamide acid is of a very precise molecular weight range, this being made possible by first reducing the aromatic dianhydride to a solution form and in excess of its solubility rate within a suitable organic solvent, and immediately thereafter adding an organic diamine to produce a precursor which is more soluble within the organic solvent system.

Another important feature of the present invention is that in process of making the polyamide acid, the organic dianhydride and diamine are first added together to make a precursor and the reaction mass is then cooled by a suitable amount because the reaction is an exothermic reaction and may produce inadvertent temperature rises which affect the imidization rate. It is only after cooling the precursor reaction mass that additional organic diamine is added to convert the precursor material to the finished polyamide acid.

A further object of the present invention is to provide a novel process for producing polyamide acids in which all the reactants are charged to a given reaction vessel, the reactions which take place there, are all controlled according to temperature and viscosity in order that the imidization rate of the reaction product is carefully regulated and determined.

A further object of the invention is to provide a new and improved process for producing polyamide acids from a wide variety of different organic dianhydride and organic diamine materials and to apply to each of them the techniques of this invention which is to rigorously exclude water, carefully regulate the temperature and pressure at a given reaction location, by continuously monitoring both temperature and pressure, and also to carefully regulate the amount and order of the addition of reactants. In this manner, we can consistently provide on a large scale manufacturing basis a polyamide acid of controlled purity and composition.

Other objects and features of the present invention will become apparent from a consideration of the following description which proceeds with reference to the accompanying drawings.

DRAWINGS FIG. 1 is an enlarged detail view of the reaction vessel which is used for carrying out the polyamide acid reaction;

FlGS. 2 and 3 together make up the entire material handling system and apparatus for preparing the reactants and supplying them to the reaction vessel, 2 being the reaction vessel portion of the system, and 3 representing the flow of reaction product after it leaves the reaction vessel, and is further blended to the desired storable quantity of solvent and product at the desired viscosity, molecular weight distribution and composition; and,

FIG. 4 is a flow diagram illustrating the process for producing the polyamide acid, including the order of addition of reactants, the preliminary treatment of such reactants and identification of the reactants in accordance with this invention.

GENERAL DESCRIPTION OF THE INVENTION The general reaction for producing a polyamide acid may be expressed as follows, wherein there is combined an aromatic dianhydride of the formula:

1 0 0 ll Ii C ll ll 0 0 wherein R is a tetravalent radical containing at least 1 ring of 6 carbon atoms, and having a benzenoid unsaturation, the 4 carbonyl groups being attached to different adjacent carbon atoms with an aromatic diamine having the formula:

2. H N R NH wherein R is a divalent aromatic radical. The reaction product is a polyimide prepolymer composed of recurring units of the formula:

HO C C CH r l R l r t C C N R If O H H I wherein R and R have the above-identified meanings and n is an integer having an average value greater than 10 and the arrows indicate isomerism. In a typical polyimide prepolymer, there are approximately 2 carboxyl groups per repeating unit and the polymer has an apparent molecular weight in excess of 15,000 as determined by intrinsic viscosity measurements made in accordance with well known teachings.

Generally speaking, we employ two moles of aromatic dianhydride (X) with one mole of diamine (Y) to yield the precursor XYX, which is more soluble in the organic solvent, this reaction being an exothermic reaction which must be carefully controlled in order to prevent undue imidization.

Initially, the aromatic dianhydride (X) is added to the organic solvent in an amount which is in excess of the solubility rate of the (X) in such solvent. ln quick succession, the diamine (Y) is added before the (X) can precipitate as an unworkable cheese like precipitate. The precursor material is formed immediately upon the addition of (Y) to the solvent which is supersaturated with (X), and the addition is done quickly enough so that the (X) will not precipitate as an unreactive, cheesy-like precipitate.

It is much easier to control imidization reaction by forming the precursor (XYX) than it would be to add the stoichiometric amount of (Y) to (X). The (Y) added is only one-half the stoichiometric amount so that the reaction of X /2 Y can be cooled more easily within the reaction vessel. The precursor units are stable molecules (see U.S. Ser. No. 822,899) and represent a controllable check point in flow sheet where temperature adjustment can be made. It is necessary to maintain the temperature as low as possible and within the range desired in order to reduce the occurrence of imidization. In some instances a certain degree of imidization is desirable since it plays a role in determination of viscosity of the ultimate product as cited in Ser. No. 822,899. The [XYX] precursor material, after having been cooled to a preferred temperature is then zipped up to form the complete polymer by adding (Y) reactant very slowly to [XYX] in substantially stoichiometric amounts while at the same time cooling, in order that the exothermic reaction will not excessively heat up the reaction mass and produce uncontrolled imidization.

Thereafter, the [XYXY] may be endcapped by adding a slight excess of (Y) in order that an anhydride group is not disposed as a terminal group, and the reaction mass is then treated with a suitable base such as ammonia or equivalent to make the product water soluble. Water then displaces some of the organic solvent which is considerably more expensive a solvent than water, and also makes the product indefinitely storable since it is immune to water as an objectionable contaminant.

Under the following headings which appear hereafter,.there is separately considered the parameters of reactants, solvents and ammonia addition to make the product water soluble.

AROMATIC DIANHYDRIDE REACTANT The aromatic dianhydrides that are useful in the process of this invention are those having the formula wherein R is a tetravalent radical containing at least one ring of 6 carbon atoms and having benzenoid unsaturation, each pair of carboxyl groups being attached to different adjacent carbon atoms. These dianhydrides include, for example, pyromellitic dianhydride, 2, 3, 6, 7-naphthalenetetracarboxylic dianhydride, 3,3'4.4'- benzophenonetetracarboxylic dianhydride, benzenel,2, 3,4-tetracarboxylic dianhydride, bis (3,4- dicarboxy phenyl) sulfone dianhydride, bis (3,4- dicarboxyphenyl) methane dianhydride, bis (2,3- dicarboxyphenyl) methane dianhydride, 2,6- dichloronaphthalene-l,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-

tetracarboxylic dianhydride, naphthalene-l,2,4,5- tetracarboxylic dianhydride,3,3 ',4,4-diphenyltetracarboxylic, dianhydride, l,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-diphenyltetracarboxylic dianhydride, 2,2'bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,l0-phenylenetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, 2,2,-bis (2,3 dicarboxyphenyl)propane dianhydride, l,l-bis (2,3-dicarboxyphenyl) ethane dianhydride, l,lbis (3,4-dicarboxyphenyl) ethane dianhydride, and the like.

ORGANIC DIAMINE REACTANT The organic diamines that are useful in the process of this invention are those having the formula:

H NRNH wherein R is a divalent radical selected from the class consisting of i wherein R' and R"" are an alkyl or an aryl group having 1 to 6 carbon atoms, n is an integer of from 1 to 4 and in has a value of 0,1 or more, and

wherein R" is selected from the group consisting of carbon in an alkylene chain having 1-3 carbon atoms,

- oxygen, silicon, phosphorous, and sulfur in III wherein R' and R"" are as above-defined and x is an integer of at least 0.

Specific diamines which are suitable for use in the present invention are: meta-phenylene diamine, paraphenylene diamine, 4,4-diamino-diphenyl propane, 4,4-diamino-diphenyl methane, benzidine, 4,4'- diamino-diphenyl sulfide, 4,4 diaminodiphenyl sulfone, 3,3 -diamino-diphenyl sulfone, 4,4 -diamino-diphenyl ether, 2,6 diamino-pyridine, bis-(4-aminophenyl) diethyl silane, bis (-4 amino-phenyl) phosphine oxide,

bis-(4-amino-phenyl) -N-methylamine, l,5-diamino naphthalene, 3,3'-climethyl-4,4', -diamino-biphenyl- 3,3 dimethoxy benzidine, m-xylylene diamine, pxylylene diamine, 1,3,-bis-delta-aminobutyltetramethyl disiloxane, l-3-bis-gamma-aminopropyltetraphenyl disiloxane, and mixtures thereof.

SOLVENT ADDITION The solvents useful in the solution phase of this invention are organic solvents whose functional groups do not react with either of the reactants (the diamines or the dianhydrides) to any appreciable extent. Besides being inert to the system and preferably, being a solvent for the polyamide acid, the organic solvent must be a solvent for at least one of the reactants, and preferably for both of the reactants. The organic solvent is an organic liquid other than either reactant or homologs of the reactants, that is a solvent for at least one reactant, and contains functional groups, the functional groups being groups other than monofunctional primary and secondary amino groups and other than the dicarboxylanhydro groups. Such solvents include dimethylsulfoxide. N-methyl-Z-pyrrolidone, the normally liquid organic solvents of the N, N-dimethyl acetamide, N-methylcaprolactam, etc. and tetramethylene urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylene-sulfone, formamide, nmethylformamide, butyrolactone, and N-acetyl-Z- pyrrolidone. The solvents can be used alone, as mixtures or in combination with poor solvents such as benzene, toluene, cresylic acid, xylene, dioxane, cyclohexane, or benzonitrile.

AMMONIATING COMPOUNDS The nitrogen containing bases that are useful in the process of this invention include, ammonia (N 1 ammonium hydroxide (NH oH), ammonium carbonate ICU [(NH CO and primary and secondary aliphatic amines containing up to 8 carbon atoms such as methylamine, ethylamine, secondary butylamine, isopropylamine, dimethylamine, diethylamine, dibutylamine, etc.

. omatic The method of synthesis in each case is to produce the precursor from the aromatic dianhydride (x) and the aromatic diamine (Y) to form [XYX], it being understood that with these small prepolymeric units, imidization is not only more controllable to achieve the correct degree of control in the viscosity of the coating solution, but also we can form mixed polymers by adding other prepolymer units of different composition, as for example [XYX] or [Y'XY'] or [XY'X] or [YX'Y] and blend these materials as required.

As a specific example of the invention, we use the ardianhydride 3,3';4,4 benzophenonetetracarboxylic dianhydride (BPDA) or (B) having the formula:

and the aromatic diamine is 4-4 methylenedianiline (MDA) or (M) having the formula:

the reaction product of the two materials where there are two moles of BPDA for each mole of MDA expressed in the following:

and the following represents the fully imidized form of the molecule In any event, with any of the foregoing techniques, we have found that to obtain a maximum degree of flexibility, toughness, dielectric strength, concentricity, heat resistance, abrasion resistance and the like, we provide the ability to form high molecular weight poly imide enamels within a narrow range of molecular weights and those results are achieved by slowly adding (M) to [BMB] precursor polymeric materials or adding {B} to [MBM] solution with the reactions being represented by:

I. nBMB nM [BMBM],,

2. nMBM nB [MBMB],,

PROCESS OF PRODUCING POLYAMIDE ACIDS AND APPARATUS Referring now to the drawings, a reaction vessel designated generally by reference numeral is jacketed and contains an inner vessel 12 and a spaced outer wall 14 with a space 16 for coolant l7 therebetween which consists of circulating water starting from an inlet 18 and a movable outlet arm 20 which provides an outlet for the cooling water. The arm 20 is pivoted at 22 on a seal joint 24 with the angular position of 20 determining the height of the coolant within the jacket or annular space 16 between vessel 12 and 14. The purpose of having variable height is that we prefer to limit the height of the coolant within the jacket to be at all times at the same height as the reaction mass within the vessel. Within the vessel are two agitators, 28 and 30, the agitator 30 being especially adapted for high viscosity mixing and the agitator 28 being for low viscosity mixing and adapted to operate at substantially greater speed.

Agitator 30 includes a stainless steel shaft 29 having four spaced blades 32 located at 90 degree intervals. Internally of the shaft 29 is a central cooling passage 34 through which cooling fluid is injected into the agitator and connecting with passages 36 extending the length of the respective blade 32, at the end of which the flow is reversed and passes into return passages 38 and then to annular passage 40, also internally of the shaft. Referring to the upper portion of FIG. 1, arrow 42 designates the inflow of cooling water and arrow 44 the outflow. In this manner, continuous circulation of cooling fluid is provided and circulated through the internal portion of the reaction vessel by means of the agitator 30 to closely control the temperature of the reaction mass. The flow rate and temperature of the coolant is in accordance with the temperature maintained in the reaction mass.

A rotary seal (not shown) is provided between the stationary portion 60 and rotatable portion 62, and the shaft 29, is supported on tapered roller bearings 61 of a support 63.

The rotatable portion 62 is driven by a high torque hydraulic motor 64 nominally rated at about hp and driven at 0-25 rpm with 7350 feet pounds of torque. The motor is mounted through pedestal 66 on upper frame 68 having cross beam reinforcement 70 which connects with cover plate 72. A coupling 73 connects motor 64 and shaft 29 through bearings 61 in bearing support 63. The cover plate 72 can be swung between open and closed position to provide for cleaning of the internal portion of the vessel.

The agitator is capable of being turned through viscosities of up to 2,000,000 centipoise and cooling is continuously effected directly upon the reaction mass through the agitator blades 32 which are immersed within the reaction mass 71 which is also cooled around the outer surface of the vessel by the water coolant, in jacket 16.

The second agitator 28, which is a high speed agitator is mounted on the frame 68, and is supported by a gusset plate 74. A hydraulic motor 76 normally rated at 40 hp. produces speeds from zero to 1400 rpm and I700 inch-pounds torque. Propeller shaft 28 has a disc-like 14 inch propeller agitator 80 which is located below the surface of the reaction mass 71 and is adapted to rotate at substantial speeds when the viscosity of the reaction mass is reduced. The agitator is supported and is elevatable by a lift cylinder 81 which raises and lowers the agitator within the reaction mass.

Referring next to FIGS. 2 and 3, the solvent is contained within a storage vessel charged through an inlet 91 and withdrawn through an outlet line 92 controlled by a valve 94. A pump 96 passes the solvent through molecular sieve particles of synthetic zeolite having a pore diameter of 3 Angstrom and designated generally by reference numerals 98 and [00 within columns 102 and 104 respectively. The upper end of the column 102 is connected by the line 108 to the lower end 110 of column 104. After passing through the molecular sieve, to remove substantially all of the water content of the solvent (having a residual [00-200 ppm), the solvent is next passed through a filter 112 in line 114 having a sample tap H6 and through a meter 1 18 to line where it discharges at 122 into the reaction vessel.

The solvent, which may consist for example of N-methyl-2-pyrrolidone (NMP) after having passed through the 3 Angstrom molecular sieve bed 98,100, is virtually water free and contamination free. The vessel is charged with an artificial atmosphere consisting of pure dry nitrogen. The nitrogen is supplied from a tank 128 through line 130 controlled by valve 132 and having an inlet 134 to the interior of the vessel. The air, including moisture, is replaced by nitrogen which is essentially water-free and, because the moisture is completely excluded, this precludes polymer chain stopping from that source of contamination.

The aromatic dianhydride and diamine are provided from one or the other of two vibrating powder hoppers 135 and 137, each having a discharge line 139 opening at 136 as indicated by arrows 138. Each of the hoppers 135, 137 contains a motor vibrator to keep the powder settled at the bottom of the discharge hopper and to insure a complete discharge thereof. The powders are supplied from a movable hopper (FIG. 2, 3) the dianhydride powders having been first thoroughly dried in a heating oven indicated by reference numeral I65 and then weighed on the scale 166 to insure the correct amount in the movable hopper 160 which is mounted on an overhead rail 167 to facilitate transport to the reaction vessel.

The dry powder resin material, when consisting of benzophenonetetracarboxylic dianhydride (BPDA), is heated and washed with acetone. As furnished the (BPDA) has approximately 2.5 percent impurities principally as benzophenonetetracarboxylic acid. The acid is removed by washing with acetone and then heating for approximately one hour at 200C. The acetone rinse may in some cases be omitted, and lower heating temperatures than 200C are also usable. but for equivalently longer periods.

The sequence of adding the reactants is important to the invention. The reaction vessel is first charged with a suitable quantity of solvent and the (BPDA) is then added up to 33 percent by weight of the solvent. Since the extent of solubility of the (BPDA) within the solvent is only approximately ]7-20 percent, the excess (BPDA) appears as a fine slurry within the supersaturated NMP solvent. The slurry has a substantial viscosity that rises to approximately 1,000 centipoises viscosity. During this solubilizing stage for the (BPDA), the exothermic reaction must be carefully controlled to avoid imidization of the (BPDA).

Thus, the jacketed vessel 10 is cooled by a continuous flow of water through the annular jacket 16 and also through the impellers 32 which are continuously rotated within the reaction mass to effect uniform cooling throughout the reaction mass and to obtain a uniform distribution of molecular weight. If localized overheating did occur, there would be a non-uniform reaction product. The supersaturated NMP will quickly produce a precipitate of the (BPDA) which will form a complex ion with itself and develop into a chesse-like precipitate which must be discarded. Therefore, shortly after the (BPDA) addition there is added to the reaction mass a quantity of the aromatic diamine to form the precursor [BMB] or [MBM]. ln the case of methylene dianiline (MDA or M) there is added to the supersaturated solvent contained in the vessel 50 percent molar quantity of (M) to produce the precursor [BMB]. The precursor formation reaction is also an exothermic reaction and cooling is continued both through the jacket and impellers; however, the [BMB] precursor is much more soluble within the NMP solvent system and therefore the viscosity quickly reduces from about one milion centipoise to a viscosity substantially equal to that of water. The (M) may contain several percent of aniline, but this is avoided by fractional distillation so that the (MDA) is approximately 99.5 percent pure. The (MDA) is added from storage 16] together with any suitable quantity of solvent obtained from 162 and both are then transferred through line 164 and outlet 166 into the reaction vessel 10. Because of the limited time within which the diamine (MDA) can be added before the aromatic dianhydride (BPDA) precipitates to an uncontrolled condition, the subsequent addition of the diamine follows shortly upon the formation of supersaturated (NMP-BPDA) mixture. When the (MDA) is added promptly as prescribed, each mole of (MDA) will react with two moles of (BPDA) so that the undissolved (BPDA) quickly goes into solution before it further complexes and precipitates; and, the (BPDA) in solution is combined with the (MDA) to form a highly soluble [BMB] precursor molecule. Thus, the order and rate of addition of the reactants is of critical importance Also, since each of the described reactions is exothermic, care must be taken to quickly remove the heat of reaction in order that the temperature of the reaction mass does not rise to the point where imidization will occur.

After the formation of the precursor [BMB], which is commonly known as a diorthoamic acid precursor, such the precursor [BMB] is zipped up to form the finished polymer by adding the remainder of the (M) at a much slower rate in order to better control the exothermic reaction which occurs both by reason of adding the (M) to the solvent and also because of the exothermic reaction which occurs by zipping up the precursor polymer:

That is why the precursor formation and zipping up are indicated separately in FIG. 4. [n the flow sheet (FIG. 4) the exotherm is controlled by the combination jacketing and cooling of the impeller to dissipate the temperature which is produced. In any event, the temperature rise will not be above the temperature of imidization. Also it is the practice, after the final polymerization reaction, to endcap the product. By adding a slight excess of M there is assured a terminal amine group, and the reaction generally may be expressed as the following:

n [BMB] +n M [BMB M1,, and, [BMBM], M

M-f-BMBM] which may be represented by the formula:

By so endcapping the product to achieve a more stable material the formulator has greater control of viscosity and molecular weight.

The endcapping can occur either in the reaction vessel 10 or vessel 212 whichever is preferred.

As described, the process occurs semi-continuously, that is, a batch of the reactant is made and the reaction vessel can discharge to be followed immediately upon recharging and resynthesis of additional batches of material.

The interval between forming the slurry (BPDA) in NMP, and the additional of (MDA) is only a matter of a few minutes, and during this period as well as all other matic solvents such as xylene and higher boiling homologs.

We have also found it feasible to replace some of the NMP with water as a solvent. This occurs by first forming ammonium polyorthoamate by the addition of ammonium hydroxide or by suitably reacting the carboxylic sites with another nitrogen base in accordance with the following general reaction:

wherein R and R are as prior-defined and y is an integerin excess of ID, for example, from [0 to l0,000 or more, and wherein from 65 to I00 percent of the total number of the [COOH] groups are in the form of the ammonium salt.

The co-diluents, ammonia or other base material derived from supply container 178 and 180 are added to a blending vessel 182 through valve controlled lines 184, 186, and are thoroughly mixed by agitator 188. The combination is then supplied through line 190 controlled by valve 192 and pump 194 through inlet line 196 and outlet opening 197 to the reaction vessel 10.

The line 190 may also serve as an inlet for such additives as an adduct of nonyl phenyl ethylene oxide which serves as a surfactant.

Generally speaking, the ammonium hydroxide is added in a controlled amount which is slightly less than having an impeller 232 on a shaft 234 and which is powered by an electric motor or the like. Additional ammonium hydroxide can be added through line 250, either separately or with other additives obtained from a blender 252, and supplied through line 259, the two lines 250, 259, being controlled by valves and 260 respectively. The blending of ammonium .lydroxide with additional water, organic solvents or a mixture of water and organic solvents with the ammonium hydroxide. After the blending occurs within the blend vessel 212, the resulting product is discharged through line 270 under the action ofa pump 272, past filter 274 and into storage containers 276.

SPECIFIC EXAMPLES Example l 20,250g of NMP was passed through a 3A molecular sieve and put in the reactor which was previously cleaned, rinsed with acetone, and purged with dry nitrogen. Agitation was started and to this 5 6,246 g of(BPDA) which had been purified by washing 0 purged with dry nitrogen and closed immediately after the stoichiometric amount that makes the polymer so completely water soluble and stops all further reactions between the BPDA and MDA. The resulting product is stable on storage and, being a water soluble material, has lower flammability, less adverse effects on contact with persons who are susceptible to dermatitis, the incidence of air pollution is reduced from fumes, and thereafter any equipment which is used with the resulting material is water cleanable.

The mixing of reactants occurs at high speed; first low viscosity high speed mixer 28, then high viscosity low speed mixer 30 having the impeller 32. After the product is produced, it is removed through discharge line 198 and outlet port 200, controlled by valve 202. A pump 204 positively displaces the reaction product indicated by the arrow 206 (FIG. 2) and it discharges into a vessel 212 where further additives may be added from storage 214 having a control valve outlet 216 and supply line 218 connecting with the vessel 212. Further mixing can occur within the vessel by an agitator 230,

additions. Immediately on addition of the (MDA) water was run through the cooling jacket. Five minutes after starting, from F, the reaction mass had reached its peak temperature of l22F. After l2 minutes the reaction mass had cooled to l00F. 1878 g of (MDA) was then added over the next 20 minutes, at which time the indicated temperature was I 10F. Following this the rate of agitation was lessened for two hours and was shut off for sixteen hours. At this time the high speed agitator was run again, bringing the temperature to 43C, at which time a sample was taken which had an absolute viscosity of l7000 poise at 43C, and an inherent viscosity of 0.86 in NMP at 0.5 g/deciliter at 37.7C.

A mixture of 5500 g (NMP) and 8000g n-butanol was then added and mixed until homogeneous. Then a mixture of l400g of 28 percent ammonium hydroxide in 4500g of distilled water was added, then a mixture of 157g ammonium hydroxide in 13,000g water, then a solution of wetting agent in lOOOg. NMP.

When coated on aluminum or copper wire, baked at 300C for an appropriate time, this polymer produced a coating which showed no failures in transformers tested in excess of 1800 hours at 325C and 300C.

Example 2: 20,250g. of NMP was passed through 3A molecular sieve and put in a clean dried and purged reactor as above. 624g of (BPDA) was added which had been purified by heating at C for 2 hours only. The same amounts of (MDA), 735g, I200 g, and l878g.

were added as in Example 1. After 2 9% hours the absolute viscosity was:

1 120 poise 65C 1720 poise 54 2250 poise 47 3200 poise 42 6000 noise 30 and the inherent viscosity was 0.57 377C and 0.5g./deciliter. g. of (BPDA) dissolved in 200g NMP was then added, at which time the absolute viscosity rose instantaneously to 4200 poise 57 and the inherent viscosity to 0.76 37.7 at 0.5g./deciliter. Solvents were added as in Example l.

Example 3: 20,250g NMP. 6246g(BPDA), 735, 1200, and l878g. MDA were treated and added as in Example 1. After one hour the absolute viscosity was:

2600 poise 665C.

3700 poise 57 7000 poise 47 13,200 poise 36 18,200 poise 31 and the inherent viscosity was 0.86 377C, with 0.5g/deciliter NMP. A solution of 20g. (BPDA) in lOOOg NMP was added and agitated for another hour, at which time the absolute viscosity was:

6500 poise 54 8800 poise 49 l0800 poise 44C l9000 poise 32C The inherent viscosity was 0.9l measured as above. 34.608g. NMP plus surfactant was added as diluent or let-down solvent.

The foregoing examples are to be construed as illustrations and not as limitations of the present invention.

It is reasonably to be expected that those skilled in this art can make numerous adaptations and revisions of the invention and it is intended that such revisions and adaptations will be included within the scope of the following claims as equivalents of this invention.

What I claim is:

l. A process for producing a polyamide resin from an aromatic dianhydride and an aromatic diamine comprising the steps of adding to a reaction vessel an essentially anhydrous organic solvent having functional groups which are nonreactive with the polymerforming reactants and a solvent for at least said aromatic dianhydride; adding to the solvent an anhydrous aromatic dianhydride in powder form; and thereby forming a slurry of such aromatic dianhydride within said solvent by combining therewith a measured amount of the aromatic dianhydride which is in excess of its solubility limits within said solvent; charging to said vessel a quantity of aromatic diamine in close succession to the formation of said slurry before said slurry precipitates into an insoluble mass; converting by condensation reaction a difunctional diprimary diamine and aromatic carbocyclic dianhydride to form a diorthoamic acid precrusor compound having a greater solubility in said solvent than either of said reactants; said compound being of molar proportions consisting of two parts of one of said reactants to one part of the other of said reactants; and controlling the temperature of the mixture within said reaction vessel by cooling the reaction mass to maintain a temperature below the imidization temperature of such reaction product.

2. The process in accordance with claim 1 including the step of: heating aromatic dianhydride prior to its introduction into said reaction vessel to render it substantially water free.

3. The process in accordance with claim 1 including the step of rendering the organic solvent substantially anhydrous by passing such solvent through a 3A molecular sieve to lower the water content to a range of between about l00-200 ppm.

4. The process in accordance with claim 1 including the step of regulating the temperature of the reaction mass which is heated by the heat of reaction of:

a. the reactants, and

b. in the formation of the precursor to determine the degree of imidization of said polyamic (amideimide) reaction product.

5. The process in accordance with claim 1 including the step of forming the slurry and precursor to a viscosity of approximately 1,000 centipoise or less, coupling the precursor to a viscosity of 4,000,000 centipoise and thereafter reducing the viscosity by the addition of ammonia water and alcohol, and continuing to agitate the reaction mass at a substantially greater rate with additional agitation means.

6. The process in accordance with claim 1 wherein the steps are performed sequentially, and in situ while maintaining the reaction product within said vessel.

7. The process in accordance with claim 1 wherein said aromatic diamine is selected from the group consisting of m phenylenediamine, 4,4 oxydianiline 4,4 sulfonylolaniline, 4,4 methylenedianiline 4,4 diamino-diphenyl sulfide 3,3 diamino-diphenyl sulfone 4,4 -diamino-diphenyl ether 2,6 diamino pyridine bis (4 amino-phenyl) diethyl silane bis (4 amino-phenyl)-N-methylamine 1,5 diamino naphthalene 3,3 dimethyl-4,4'-diamino-biphenyl 3,3 dimethoxy benzidine m xylylene diamine p xylylene diamine 1,3 bis-delta-amino butyltetramethyl disiloxane and, 1,3 bis-gamma-amino propyl tetraphenyl disoloxane and mixtures thereof 8. The process in accordance with claim 1 wherein said aromatic dianhydride is represented by the general formula wherein R is an organic tetravalent radical containing at least one ring of 6 carbon atoms and having benzenoid unsaturation, the 4 carboxyl groups of each unit being attached directly to separate carbon atoms, each pair of carboxyl groups being attached to adjacent carbon atoms in a ring of the R radical.

9. A process in accordance with claim I wherein said solvent is selected from the group consisting of: dimethylsulfoxide, N-methyl-Z-pyrrolidone, N,N-dimethylmethoxyacetamide, N-caprolactam, tetpoises or less.

11. The process in accordance with claim 1 including the step of initially stirring the mixture of aromatic dianhydride and solvent at a relatively low speed and stirring the mixture of aromatic dianhydride and aromatic diamine at a substantially faster speed when such mixture is converted to a precursor of substantially less viscosity. 

1. A PROCESS FOR PRODUCING A POLYAMIDE RESIN FROM AN AROMATIC DIANHYDRIDE AND AN AROMATIC DIAMINE COMPRISING THE STEPS OF ADDING TO A REACTION VESSEL AN ESSENTIALLY ANHYDROUS ORGANIC SOLVENT HAVING FUNCTIONAL GROUPS WHICH ARE NONREACTIVE WITH THE POLYMER-FORMING REACTANTS AND A SOLVENT FOR AT LEAST SAID AROMATIC DIANHYDIDE; ADDING TO THE SOLVENT AN ANHYDROUS AROMATIC DIANHYDRIDE IN POWDER FORM; AND THEREBY FORMING A SLURRY OF SUCH AROMATIC DIANHYDRIDE WITHIN SAID SOLVENT BY COMBINING THEREWITH A MEASURED AMOUNT OF THE AROMATIC DIANHYDRIDE WHICH IS IN EXCESS OF ITS SOLUBILITY LIMITS WITHIN SAID SOLVENT; CHARGING TO SAID VESSEL A QUANTITY OF AROMATIC DIAMINE IN CLOSE SUCCESSION TO THE FORMATION OF SAID SLURRY BEFORE SAID SLURRY PRECIPITATES INTO AN INSOLUBLE MASS; CONVERTING BY CONDENSATION REACTION A DIFUNCTIONAL DIPRIMARY DIAMINE AND AROMATIC CARBOCYCLIC DIANHYDRIDE TO FORM A DIORTHOAMIC ACID PRECRUSOR COMPOUND HAVING A GREATER SOLUBILITY IN SAID SOLVENT THAN EITHER OF SAID RECTANTS; SAID COMPOUND BEING OF MOLAR PROPORTIONS CONSISTING OF TWO PARTS OF ONE OF SAID REACTANTS TO ONE PART OF THE OTHER OF SAID REACTANTS; AND CONTROLLING THE TEMPERATURE OF THE MIXTURE WITHIN SAID REACTION VESSEL BY COOLING THE REACTION MASS TO MAINTAIN A TEMPERATURE BELOW THE IMIDIZATION TEMPERATURE OF SUCH REACTION PRODUCT.
 2. The process in accordance with claim 1 including the step of: heating aromatic dianhydride prior to its introduction into said reaction vessel to render it substantially water free.
 3. The process in accordance with claim 1 including the step of rendering the organic solvent substantially anhydrous by passing such solvent through a 3A molecular sieve to lower the water content to a range of between about 100-200 ppm.
 4. The process in accordance with claim 1 including the step of regulating the temperature of the reaction mass which is heated by the heat of reaction of: a. the reactants, and b. in the formation of the precursor to determine the degree of imidization of said polyamic (amide-imide) reaction product.
 5. The process in accordance with claim 1 including the step of forming the slurry and precursor to a viscosity of approximately 1,000 centipoise or less, coupling the precursor to a viscosity of 4,000,000 centipoise and thereafter reducing the vIscosity by the addition of ammonia water and alcohol, and continuing to agitate the reaction mass at a substantially greater rate with additional agitation means.
 6. The process in accordance with claim 1 wherein the steps are performed sequentially, and in situ while maintaining the reaction product within said vessel.
 7. The process in accordance with claim 1 wherein said aromatic diamine is selected from the group consisting of m - phenylenediamine, 4,4'' oxydianiline 4,4'' - sulfonylolaniline, 4,4'' methylenedianiline 4,4'' - diamino-diphenyl sulfide 3,3 - diamino-diphenyl sulfone 4,4'' -diamino-diphenyl ether 2,6'' - diamino pyridine bis - (4 amino-phenyl) diethyl silane bis - (4 amino-phenyl)-N-methylamine 1,5 - diamino naphthalene 3,3'' - dimethyl-4,4''-diamino-biphenyl 3,3'' - dimethoxy benzidine m xylylene diamine p - xylylene diamine 1,3 - bis-delta-amino butyltetramethyl disiloxane and, 1,3 - bis-gamma-amino propyl tetraphenyl disoloxane and mixtures thereof
 8. The process in accordance with claim 1 wherein said aromatic dianhydride is represented by the general formula
 9. A process in accordance with claim 1 wherein said solvent is selected from the group consisting of: dimethylsulfoxide, N-methyl-2-pyrrolidone, N,N-dimethylmethoxyacetamide, N-caprolactam, tetramethylene urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylenesulfone, formamide, N-methylformamide, butyrolactone, N-acetyl-2-pyrrolidone, and mixtures thereof in combination with benzene, toluene, cresylic acid, xylene, dioxane, cyclohexane, and benzonitrile.
 10. The process in accordance with claim 1 wherein the extent of aromatic dianhydride addition within said solvent produces a viscosity in the order of 1,000 centipoises or less.
 11. The process in accordance with claim 1 including the step of initially stirring the mixture of aromatic dianhydride and solvent at a relatively low speed and stirring the mixture of aromatic dianhydride and aromatic diamine at a substantially faster speed when such mixture is converted to a precursor of substantially less viscosity. 